This invention relates to a substrate of a photosensitive web material and a core for a photosensitive web material which improves marking troubles of the photosensitive web material formed near the core.
The substrate base end of a conventional photosensitive web material is formed in almost a rectangular shape, both in the section and in the plane figure, as shown by dashed lines in FIG. 1. As a result, when conventional photosensitive web material is wound around a core, as shown in FIG. 13, a difference in level is formed between the base end 4 of the web 1 and the core 11 due to the thickness t of the web 1.
The conventional core for the photosensitive web is formed by winding in spiral a dense kraft paper, regenerated paper or the like. The core is rendered as hard as possible in order to prevent deformation of the core by the winding pressure of the photosensitive web, shocks encountered during physical distribution and the like, and therefore, its flattening compressive strength is high.
Since the photosensitive web is wound tight, creases 16 (FIG. 13), patterns and pressure marks are formed in several folds of the web near the core by the difference in levels at the base end portion of the web, the spiral groove on the surface of the core, etc. Moreover, in the case of fixing the base end of the photosensitive web using an adhesive, tape marks were also formed. These marks are formed during winding the photosensitive web and during preservation by the winding tension and its own weight.
The occurrence of these marks can be reduced to a certain degree by winding loosely. However, the loosely wound photosensitive web tends to project in a form of a cone by shaking during distribution, inclined state or the like. Moreover, wound form tends to be defective, and packaging defects also tend to be generated. As a result, workability is shaply decreased. An optimal roll density is determined by the thickness, length and friction coefficient of the photosensitive web, the flexibility and surface hardness of the substrate, temperature, humidity, distribution means, time and so on, and it is difficult to determine a suitable roll density.
A means for resolving the problem to form marks by the difference in level by the base end of the web is disclosed in Japanese Utility Model KOKAI Nos. 57-60141 and 63-41072 which forms a step portion 17 on the core corresponding to the thickness of the web in the axial direction, as shown in FIG. 12, and the web is begun to be wound from the step portion. This means has not been put to practical use, because it is not easy to adjust the base end of the web to the step portion under a dark safety light. The manufacture of the core is a special order, and the height of the step must be changed according to the thickness of the web. As a result, the manufacturing cost of the core is expensive.
Another means for resolving the problem is to form marks by the difference in level by the base end of the web as disclosed in Japanese Utility Model KOKAI No. 53-32021 wherein the base end of the web is cut obliquely in the plane figure. In this means, workability is improved, because the positioning of the base end of the web is easy. The occurrence of marking troubles is reduced to a certain degree, but the occurrence of pressure marks still remains due to the rectangular cutting in the thickness direction.
A means for resolving the problem due to the hardness of the core surface is disclosed in Japanese Utility Model KOKOKU No. 2-24116 which covers the circumferential face of the core in the whole width with a sheet having cushioning characteristics and elasticity, such as low density papers of less than 0.5 g/cm.sup.3, synthetic papers and foamed resin sheet having an expansion ratio of 5 to 15 times. When the above core covered with the foamed resin sheet or the like is used as the core for a roll of photographic printing paper where a photographic emulsion layer is coated on a paper substrate or a water-resistant substrate made of paper of which both side are coated with various polyethylene resins, various physical marking troubles and pressure mark troubles can sharply be reduced. On the other hand, when the above core is used as the core for a roll of a photographic film of which the substrate is a plastic film having a less elasticity than the paper substrate, the marking troubles and pressure mark troubles occur in 5 to 6 revolutions of the film from the base end of the film. The Japanese Utility Model KOKOKU No. 2-24116 discloses a core provided with nonwoven fabric. In this core, since the friction resistance is small between the photographic film and the nonwoven fabric, it is necessary to fix the photographic film to the nonwoven fabric using an adhesive tape.